Method of forming a hydraulic damper

Abstract: A hydraulic damper (10) for a motor vehicle comprising a longitudinally extending tube (12) and a separately formed spring seat (50) positioned on the tube, wherein the tube is formed from extruded aluminium or aluminium alloy, and the spring seat is formed from aluminium or aluminium alloy.

Description: This invention relates to a method of forming a hydraulic damper. By hydraulic damper is meant a suspension strut or shock absorber. A hydraulic damper for use in the suspension system of a motor vehicle typically comprises a tube; a piston sealably slidably mounted in the tube and attached to a piston rod, the piston separating a compression chamber from a rebound chamber within the tube; a compression stroke valve mounted on the piston which allows fluid flow from the compression chamber to the rebound chamber; and a rebound stroke valve mounted on the piston which allows fluid flow from the rebound chamber to the compression chamber. The piston rod extends out of the tube at one end thereof, and is sealably slidably mounted in that one end. Such hydraulic dampers either comprise an inner tube and an outer tube (sometimes referred to as a twin tube damper) in which the piston sealably slides in the inner tube, or comprise a single tube (sometimes referred to as a monotube damper). It is usual practice to form the or each tube of a hydraulic damper by rolling a sheet of steel and welding together the adjacent longitudinal edges. External parts, such as the spring seat and the mounting bracket or steering knuckle, which are also formed from steel, are then welded to the single tube or the outer tube. The other end of the tube is sealed closed by welding on an end plate or by arc-heating and rolling the tube end, and the internal components of the suspension strut (such as those mentioned above) are inserted into the tube by way of the one end thereof, which is then sealed closed. The use of several welding steps has disadvantages in that welds are time consuming operations. Further, welds are susceptible to corrosion. Still further, the use of steel has disadvantages with regard to weight. DE-A-4129644 discloses a method in accordance with the preamble of claim 1. It is an object of the present invention to overcome one or more of the above mentioned disadvantages. A method of forming a hydraulic damper in accordance with the present invention comprises extruding a tube of aluminium or aluminium alloy; forming a spring seat of aluminium or aluminium alloy; positioning the spring seat on the extruded tube; and closing an end of the extruded tube by flame heating the end of the extruded tube and rolling the flame heated end. This invention removes the steps of welding, thereby removing time consuming operations. Further the use of aluminium or aluminium alloy has advantages with regard to weight when compared to previously known arrangements. The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a perspective view of a hydraulic damper in accordance with the present invention; Figure 2 is a cross-sectional view of the hydraulic damper of Figure 1 with the spring seat and its attachment arrangement omitted for clarity; Figure 3 is a cross-sectional view of the spring seat and extruded tube of the hydraulic damper of Figure 1; Figure 4 is a cross-sectional view similar to that of Figure 3 showing an alternative arrangement for securing the spring seat; Figure 5 is a cross-sectional view of apparatus for forming the beads shown in Figures 3 and 4; Figure 6 is a partial cross-sectional view of an alternative embodiment of hydraulic damper in accordance with the present invention; Figure 7 is a cross-sectional view of the extruded tube of the hydraulic damper of Figure 6 taken on the line VII-VII; Figure 8 is an end view of the spring seat of the hydraulic damper of Figure 6; and Figure 9 is a side view of the spring seat of Figure 8. Referring to the Figure 2 of the drawings, the hydraulic damper 10 shown is of the twin tube damper type, and comprises an outer tube 12, and an inner tube 14 substantially coaxial with the outer tube on an axis L. The outer tube 12, and preferably the inner tube 14, are formed from extruded aluminium or aluminium alloy and have a substantially constant cross-section along their length. The hydraulic damper 10 further comprises conventional components such as a piston assembly 16, a piston rod 18 having a longitudinal axis on axis L, a compensation valve 20, and a rod guide 22. The piston assembly 16 includes a compression valve and a rebound valve (not shown). The piston assembly 16, the compensation valve 20 and the rod guide 22 may be any suitable conventional design well known to those skilled in the art, and will not be described in detail. The inner tube 14 is substantially closed at one end 24 by the compensation valve 20, and is substantially closed at the other end 26 by the rod guide 22. The outer tube 12 is closed at one end 28 by flame heating and rolling the outer tube walls, and is substantially closed at the other end 30 (the open end) by the rod guide 22 and by spin closing the end 30 of the outer tube as. An example of apparatus suitable for spin closing is disclosed in our GB patent application no. 9412806.3 (2290736 A), published after the priority date of the present application, in which a pair of rollers initially push a portion of the outer tube at the open end over at approximately 45°, and a second pair of rollers then push a section of the portion over at approximately 90°, whilst the outer tube is spinning about its longitudinal axis. The piston rod 18 extends through, and makes a sealing sliding fit with the rod guide 22. The piston assembly 16 makes a sealing sliding fit with the inner surface 32 of the inner tube 14. The piston rod 18 is secured to the piston assembly 16 by a nut 34 or any other suitable means. The piston assembly 16 divides the inner area of the inner tube 14 into a rebound chamber 36 and a compression chamber 38. The area between the inner tube 14 and the outer tube 12 defines a compensation chamber 40. The rebound and compression chambers 36 and 38 are substantially filled with fluid to damp reciprocating movement of the piston assembly 16 and piston rod 18 along axis L relative to the outer and inner tubes 12 and 14. The compensation chamber 40 is partly filled with fluid and acts as a reservoir for the fluid in the rebound and compression chambers 36 and 38. The hydraulic damper 10 is mounted in a motor vehicle (not shown) using mounting means in the form of a mounting bracket 46. The mounting bracket 46 is extruded from aluminium or aluminium alloy to integrally form a tubular portion 43 with a pair of spaced arms 42 which are substantially parallel. The tubular portion 43 has an internal diameter which is sized to make a close sliding fit on the outer tube 12. Pairs of holes 44 are cut in each arm 42 to form mounting apertures for the mounting bracket 46. The mounting bracket 46 is then slid into position on the outer tube 12, and is secured in place by pressing or punching a tangentially extending groove 47 in the tubular portion 43 and the outer tube 12. Other forms of mounting means may be used as an alternative to the bracket 46, or other attachment arrangements may be used besides the groove 47. As an alternative to flame heating and rolling closed the one end 28 of the outer tube 12, the one end may be sealed and closed by a separately formed end plate or by flattening the one end of the outer tube into a substantially planar formation, and then rolling the planar formation in the longitudinal direction. As a further alternative, however, a mounting means of aluminium or aluminium alloy may be cast with an integral end cap and secured to the one end of the extruded tube to seal and close the one end. A spring seat 50 is attached to the outer tube 12 as shown in Figure 1. A first external, circumferentially extending, bead 48 is formed in the outer tube 12, preferably as described below. The spring seat 50, which is of aluminium or aluminium alloy, is formed by pressing or casting and includes a cylindrical section 52 which has an internal shape and size which is substantially the same as the external shape and size of the outer tube 12 - that is, the cylindrical section can make a close sliding fit on the outer tube. The spring seat 50 is slid onto the outer tube 12, with the tube passing through the cylindrical section 52. One end 54 of the cylindrical section rests on the first bead 48. A second external, circumferentially extending, bead 56 is then formed in the outer tube 12 adjacent the other end 58 of the cylindrical section 52 to secure the spring seat 50 on the outer tube. The second bead 56 is optional and may be omitted because, in use, a coil spring (not shown) acts on the spring seat 50 to bias the one end 54 of the cylindrical section 52 into contact with the bead 48. In the modified arrangement shown in Figure 4, the spring seat 60 is slid into position before the formation of any bead or beads. One or more external, circumferentially extending, beads 62 are them formed simultaneously in the outer tube 12 and in the cylindrical section 64 of the spring seat 60 to secure the spring seat 60 in position. Preferably, two beads 62 are formed. The external circumferentially extending bead 48 of Figure 3 is preferably formed as shown in Figure 5 by positioning one end of the extruded tube 12 in a die 70 having a correspondingly shaped closed bore 72, and by positioning a pair of substantially identical dies 74 having substantially semi-circular grooves 76 therein around the extruded tube but slightly spaced from the die 70. The dies 74 are then moved towards one another to grip the extruded tube 12 and the die 70 moved towards the dies 74 to form the bead 48, the relative movement between the dies being indicated by the arrows in Figure 5. Similar arrangements can be used for forming the beads 56 and 62 of Figures 3 and 4 respectively. In a preferred arrangement, the spring seat 50 of Figure 3 is slid into position on the outer tube 12 before the formation of the bead 48. The bead 48 is then formed as described above. This arrangement reduces the risk of the outer tube 12 expanding adjacent the bead 48 (because of the presence of the cylindrical section 52 of the spring seat 50) and causing problems with any subsequent attempt to slide the spring seat into position. As an alternative to this arrangement, the spring seat 50 may be secured by forming two rings of external dimples rather than beads, or by rivets, or any other suitable alternative arrangement. Either prior to, or after, attachment of the spring seat 50, the one end 28 of the outer tube 12 is closed by flame heating the end of the outer tube, and then rolling over the end. Having formed the outer tube 12 with the mounting bracket 46 and the spring seat 50 secured thereto, and having closed the one end 28, the other components (as described above) of the hydraulic damper 10 can then be assembled therein. In the alternative embodiment of hydraulic damper 80 shown in Figure 6, mounting means in the form of a steering knuckle 82, which is cast from aluminium or aluminium alloy, is secured to one end 84 of an extruded aluminium or aluminium alloy tube 86. Other forms of mounting means may be used. A spring seat 88 which is also cast from aluminium or aluminium alloy is positioned on the extruded tube 86. As shown in Figures 8 and 9, the spring seat 88 has a shape which is similar to a spoked wheel and comprises an inner cylindrical section 90, an outer annular portion 92, and a number of spokes 94 interconnecting the cylindrical section and the annular portion. The spokes 94 have a predetermined shape and size to provide the necessary strength for the spring seat 88. The annular portion 92 provides a seat for a coil spring (not shown) on installation of the hydraulic damper 80 on a motor vehicle. The use of spokes 94 helps to reduce the weight of the spring seat 88 and the accumulation of dirt on the spring seat. As can be seen from Figure 7, the extruded tube 86 is formed with two pairs of external, longitudinally (axially) extending, outwardly directed, ribs 96,98, with the ribs of each pair being diametrically opposed, and the pairs being set at right angles to one another. The ribs 96,98 of each pair have substantially the same cross-sectional shape and area, but different from the cross-sectional shape and area of the other pair of ribs. The cylindrical section 90 of the spring seat 88 has correspondingly shaped and sized grooves 100,102 formed in its internal surface 104. This arrangement allows the spring seat 88 to make a close sliding fit with the extruded tube 86, and also provide means for correctly locating the spring seat relative to the extruded tube. A part of one or more of the ribs 96,98 is removed after extrusion of the tube 86 and a part of the corresponding groove or grooves 100,102 is omitted on casting to provide one or more pairs of engaging shoulders 106 which act as a stop to again correctly locate the spring seat 88 on the extruded tube 86. As an alternative to the above described arrangement, the extruded tube may be extruded with grooves therein and the cylindrical section of the spring seat cast with corresponding inwardly directed ribs. Referring back to Figure 6, the other end 108 of the extruded tube 86 is closed by a threaded cap 110, as an alternative arrangement to spin closing, which is screw threaded onto threads formed on the extruded tube 86. In a modification of the arrangement shown in Figures 6 to 9, the ribs and grooves are omitted, and the spring seat is cast with an integral cylindrical section and threaded cap. The end of the extruded tube is threaded as shown in Figure 6, and screw threading of the cap to the extruded tube positions the spring seat on the extruded tube. Whilst the above described embodiments refer to the twin tube type of hydraulic damper, it will be appreciated that at least some of these arrangements are also applicable to hydraulic dampers of the monotube type in which the sole tube of the damper is formed from extruded aluminium or aluminium alloy and has an aluminium or aluminium alloy spring seat positioned thereon. Preferably the extruded tube and the spring seat are formed from aluminium alloy conforming to BS 6082 and which comprises, by weight percentage, 0.70 to 1.3% Si, 0.5% Fe, 0.1% Cu, 0.4 to 1.0% Mn, 0.6 to 1.2% Mg, 0.25% Cr, 0.2% Zn, 0.1% Ti, 0.05 to 0.15% impurities, with the remainder being aluminium. Other compositions of aluminium alloy may be used. All of the above described arrangements have advantages in terms of easier manufacture and assembly, and of providing a hydraulic damper of reduced weight compared to previously known arrangements.

Claims: A method of forming a hydraulic damper (10) comprising extruding a tube (12) of aluminium or aluminium alloy; forming a spring seat (50) of aluminium or aluminium alloy; and positioning the spring seat on the extruded tube; characterised by closing an end (28) of the extruded tube by flame heating the end of the extruded tube and rolling the flame heated end. A method as claimed in Claim 1, wherein the spring seat (50) is formed by pressing. A method as claimed in Claim 1, wherein the spring seat (88) is formed by casting. A method as claimed in any one of Claims 1 to 3, wherein the spring seat (50) is formed with a cylindrical section (52) which overlies a portion of the extruded tube (12) on positioning the spring seat on the extruded tube. A method as claimed in any one of Claims 1 to 3, wherein the spring seat (88) is formed with an inner cylindrical section (90), an outer annular portion (92), and a number of spokes (94) interconnecting the cylindrical section and the annular portion. A method as claimed in any one of Claims 1 to 5, wherein the extruded tube (86) is formed with one or more external longitudinally extending ribs (96,98) which engage with corresponding grooves (100,102) formed in the spring seat (88) to locate the spring seat on the extruded tube in a predetermined position. A method as claimed in any one of Claims 1 to 5, wherein the spring seat is integrally formed with a cap for closing the other end of the extruded tube. A method as claimed in Claim 4 or Claim 5, wherein an external circumferentially extending bead (48) is formed in the extruded tube (12), and the spring seat (50) is slid onto the extruded tube until one end (54) of the cylindrical section engages the bead. A method as claimed in Claim 4 or Claim 5, wherein the spring seat is slid onto the extruded tube, and an external circumferentially extending bead is formed in the extruded tube adjacent one end of the cylindrical section. A method as claimed in Claim 8 or Claim 9, wherein a second external circumferentially extending bead (56) is formed in the extruded tube (12) adjacent the other end of the cylindrical section (52) to retain the spring seat on the extruded tube. A method as claimed in Claim 4 or Claim 5, wherein the spring seat (60) is slid onto the extruded tube (12), and at least one external circumferentially extending bead (62) is formed in the extruded tube and the cylindrical section (64). A method as claimed in Claim 6, wherein the or at least one of the ribs (96,98) is cut to define a shoulder (106), and wherein the or at least one of the grooves (100,102) is formed with a corresponding shoulder, the spring seat being slid onto the extruded tube until the shoulders engage to locate the spring seat on the extruded tube in a predetermined position.

Inventors: ARJONA ANTONIO PEREZ DE LA LAS, BARBOSA MANUEL TORNELL, FULKS GARY CHRIS, GARCIA MIGUEL CANDELA, GOROSTIDI JOSE IGNACIO MEMBRIL, JIMENEZ FRANCISCO JAVIER SANCH, JONES NICHOLAS, ARJONA,ANTONIO PEREZ DE LA LASTRA, BARBOSA, MANUEL TORNELL, FULKS, GARY CHRIS, GARCIA, MIGUEL CANDELA, GOROSTIDI, JOSE IGNACIO MEMBRILLERA, JIMENEZ, FRANCISCO JAVIER SANCHEZ, JONES, NICHOLAS
Applicants: DELPHI ESPANA AUTOMOTIVE SYS, DELPHI FRANCE AUTOMOTIVE SYS, DELPHI AUTOMOTIVE SYSTEMS ESPANA SA, DELPHI FRANCE AUTOMOTIVE SYSTEMS
Application year: 1994
Main classification: F16F9
IPC codes: B60G13, F16F9, B60G15